1. Field of the Invention
This invention relates to a focus adjustment device and method for a camera that accomplishes focus adjustment of a photographic lens to properly focus the camera on a photographic object.
2. Description of Related Art
In well known focus adjustment devices, detection of the focus adjustment state of the photographic lens is accomplished by determining a defocus amount, the defocus amount representing the difference between the image plane of the photographic object and the specified detection surface (i.e., the conjugate film surface). The photographic lens is driven based on the defocus amount to focus the camera.
In a single focus mode, the photographic lens focuses on the photographic object once, then the lens is no longer driven. In a continuous focus mode, defocus detection is repeatedly accomplished after the initial focusing, and if the amount of detected defocus exceeds upper or lower standard parameters, the lens is driven again to maintain the camera's focus on a subject. Ordinarily, the operation of the continuous focus mode is initiated by depressing a release button halfway. If the range between the upper and lower standard parameters is reduced, the camera is very sensitive to the detected amount of defocus, and the photographic lens is driven in a "hunting" state, wherein the lens is continually moving small amounts to adjust the camera's focus. On the other hand, if the range between the upper and lower standard parameters is increased, then the unstable photographic lens movements will disappear. However, if at the time of shutter release (i.e., complete depression of the release button) the camera is improperly focused, and a photograph is taken with a slight blurring due to the improper focus.